.highlight {
  position: relative;
}
.btn-copy {
  z-index: 1;
  display: inline-block;
  cursor: pointer;
  border: none;
  -webkit-appearance: none;
  font-size: 12px;
  font-weight: bold;
  padding: 3px 6px;
  color: #333;
  background: rgba(255,255,255,0.8);
  border-radius: 2px;
  position: absolute;
  top: 0;
  right: 0;
  opacity: 0;
  transition: all linear 0.2s;
}
.btn-copy >i {
  margin-right: 4px;
  font-size: 10px;
  transform: translateY(1px);
}
.btn-copy:hover {
  background: rgba(255,255,255,0.7);
}
.highlight:hover .btn-copy {
  opacity: 1;
}
.article pre:hover .btn-copy {
  opacity: 1;
}
